1. Field of the Invention
The present invention relates to a magnetic tape recording and/or reproducing apparatus such as, for example, a video tape recorder, operable with a tape cassette having supply and take-up reels and a length of magnetic recording tape secured at its opposite ends to the supply and take-up reels, respectively.
More specifically, the present invention relates to a magnetic tape recording and/or reproducing apparatus, hereinafter referred to as a magnetic tape player, of a type capable of indicating to an operator of the magnetic tape player whether or not a cassette tape loaded into the magnetic tape player has a sufficient length of magnetic recording tape to completely record thereon the entire length of that particular information, such as for example, a televised program, the operator wishes to record.
2. Description of the Background Art
A magnetic tape player having a capability of indicating the length of magnetic recording tape remaining on the supply reel or the remaining tape length is well known in the art and currently available in the market. Generally, the length of magnetic recording tape remaining on the supply reel and available for information recording or reproduction (playback) is indicated by means of a tape counter in terms of the length of time left until an approach to the end-of-tape is detected. Even though the magnetic tape player has the capability of indicating the remaining tape length, it has often been observed that the user or operator of the magnetic tape player is annoyed if the cassette tape loaded into the magnetic tape player does not have a sufficient length of magnetic recording tape required to completely record thereon the entire length of a particular televised program the operator wishes to record.
In any event, reference will be made to FIGS. 3 and 4 of the accompanying drawings for the detailed discussion of the prior art magnetic tape player believed to be closest to the present invention.
FIG. 3 illustrates both the magnetic tape player in schematic perspective representation and a circuit block diagram showing a tape transport speed selector mechanism used in the magnetic tape player. A length of magnetic recording tape is generally indicated by 1 having one end secured to a supply reel 2 to form a supply tape pack and the opposite end secured to a take-up reel 3 to form a recorded tape pack. A portion of the magnetic recording tape 1 generally intermediate between the supply and recorded tape packs on the supply and take-up reels 2 and 3 is, with respect to the direction of tape transport from the supply reel 2 towards the take-up reel 3, passed in front of an eraser head 24, then turned a predetermined angle around a rotary drum assembly 6 so as to be scanned by one or more magnetic transducing heads, passed in front of an audio eraser head 25 and an audio control head 26 and finally passed through a gap between a capstan 4 and a pinch roller 5.
The capstan 4 is drivingly coupled with a drive motor 23 which is in turn electrically connected with a tape transport means 18. Although not shown, the tape transport means 18 comprises a drive circuit and a servo control mechanism and is operable to drive the capstan drive motor 23 through the servo control mechanism so as to transport the magnetic recording tape 1 at a predetermined speed from the supply reel 2 towards the take-up reel 3. This tape transport means 18 is electrically connected with a recording timer 17 adapted to be preset with a recording time during which information recording on the magnetic recording tape 1 is desired to be made and operable to cause a recording time display unit 16 to display the balance of the preset recording time less the length of time actually spent in the information recording and also to generate a stop signal to the tape transport means 18 to terminate the tape transport when the balance of the preset recording time less the length of time actually spent in the information recording becomes zero, that is, when the length of time corresponding to the preset recording time has been passed.
The tape transport means 18 is also connected with a tape transport speed selecting means 19 including a tape transport speed selecting switch 20 capable of assuming one of at least two positions, for example, SP (Standard Play mode during which the magnetic recording tape is transported at a first or standard speed) and EP (Extended Play mode during which the length of magnetic recording tape 1 is transported at a second or extended speed which is 1/n of the standard speed, n being arbitrarily chosen integer, for example, 2 or 3) mode positions. The tape transport speed selecting means 19 is so designed as to generate an SP mode signal to the tape transport means 18 to cause the magnetic recording tape 1 to be transported at the standard speed from the supply reel 2 onto the take-up reel 3 when the tape speed selecting switch 20 is set in the SP mode position, and to generate an EP mode signal to the tape transport means 18 to cause the magnetic recording tape 1 to be transported at the extended speed from the supply reel 2 onto the take-up reel 3 when the tape transport speed selecting switch 20 is set in the EP mode position.
FIG. 4 illustrates a system for calculating the length of magnetic recording tape 1 remaining on the supply reel 2 (which length is hereinafter referred to as the remaining tape length) and the length of time corresponding to the length of magnetic recording tape remaining on the supply reel 2, which system is employed in the prior art magnetic tape player employing the tape transport speed selector mechanism shown in and described with reference to FIG. 3. This system is found in, for example, the Japanese Patent Publication Examined No. 55-34514, published Sept. 6, 1980, and U.S. Pat. No. 3,834,648, issued Sept. 10, 1974.
In FIG. 4, reference numeral 7 represents a tape motion measuring mechanism for calculating the amount of movement of the magnetic recording tape 1 in a direction longitudinally thereof; reference numeral 8 represents a calculating circuitry operable in response to an signal from the tape motion measuring mechanism 7, which signal is indicative of the amount of movement of the magnetic recording tape 1, to calculate, and generate an output signal indicative of, the remaining tape length or the length of time corresponding to the remaining tape length (which length of time is hereinafter referred to as the remaining tape hour); and reference numeral 15 represents a tape hour display unit for displaying the remaining tape hour.
With reference to FIG. 4, the method of calculating and displaying the remaining tape hour, that is, the length of time corresponding to the remaining tape length on the supply reel 2, will be discussed in detail as it pertains to the present invention.
The tape motion measuring mechanism 7 comprises a reel revolution detecting means or reel tachometer 11 for providing a signal R per revolution of the supply reel 2; a tape length detecting means 9 drivingly coupled with a drive system for the capstan 4 for providing a signal P each time a predetermined length of the magnetic recording tape 1 is moved in a direction longitudinally thereof; and a tape motion detecting means 10 operable to count the number of signals P, outputted from the tape length detecting means 9, in reference to the signal R outputted from the reel tachometer 11 and for subsequently outputting a tape length signal l representative of the length of the magnetic recording tape having been moved per revolution of the supply reel 2. The reel revolution detecting means or reel tachometer 11 may comprise a photodetector system including a light emitting element or photodiode and a light reflecting or intercepting plate secured to a drive system for the supply reel 2 and designed to generate the signal R each time the supply reel 2 undergoes a complete revolution.
The calculating circuitry 8 is connected with the tape motion measuring mechanism 7 so as to receive the tape length signal l and is operable to determine the remaining tape length Ls, then to calculate the remaining tape hour Ts on the basis of the remaining tape length Ls and to output a remaining tape hour signal, representative of the calculated remaining tape hour, which is subsequently applied to a remaining tape hour display unit 15 for the display of the remaining tape hour Ts. This calculating circuitry 8 is comprised of a squaring circuit 12, a subtracting circuit 13 and dividing circuit 14.
The calculating circuitry 8 performs the following calculations.
The remaining tape length Ls, that is, the entire length of the magnetic recording tape 1 remaining on the supply reel 2, can be expressed by the following equation. EQU Ls=.pi.(rs.sup.2 -rh.sup.2)/d (1)
where rs represents the radius of the tape pack on the supply reel 2 including the radius rh of the reel hub of the supply reel 2 as shown in FIG. 3 and d represents the thickness of the magnetic recording tape 1.
Assuming that the length of the magnetic recording tape 1 moved in the longitudinal direction thereof per revolution of the supply reel 2 is expressed by l, the parameter rs, that is, the sum of the radii of the tape pack and the reel hub, can be expressed as follow. EQU rs=l/2.pi. (2)
Rewriting the equation (1) with the use of the equation (2) results in: ##EQU1##
Since the thickness d of the magnetic recording tape 1 and the radius rh of the reel hub of the supply reel 2 are known parameters, the remaining tape length Ls can be determined if the length l of magnetic recording tape 1 moved per revolution of the supply reel 2 is determined.
Also, if the standard tape transport speed is expressed by V, the remaining tape hour Ts, that is, the length of time corresponding to the remaining tape length Ls (or the length of time over which information recording or playback can be available on the remaining tape length Ls) can be determined from the following equation. EQU Ts=Ls/V (4)
In view of the foregoing, the squaring circuit 12 of the calculating circuitry 8 is operable to determine the square of the length l of the magnetic recording tape 1 moved per revolution of the supply reel 2. The subtracting circuit 13 is operable to subtract (4.pi..sup.2 .multidot.rh.sup.2) from the squared value l.sup.2, and the dividing circuit 14 is operable to divide (l.sup.2 -4.pi..sup.2 .multidot.rh.sup.2) by 4.pi.dV to give the remaining tape hour Ts.
In the conventional magnetic tape player of the above described construction including the tape transport speed selector means 19 and the tape motion measuring mechanism 7, if the operator or user of the magnetic tape player wishes to change the tape transport speed during an information recording, he or she has to read the remaining tape hour Ts, indicated by the remaining tape hour display unit 15, and the balance of the preset recording time less the length of time actually spent in the information recording, indicated by the recording time display unit 16, and then manipulates the tape transport speed selecting switch. More specifically, assuming that the information recording is taking place with the tape transport speed set at the standard speed, that is, assuming that the information recording is taking place with the magnetic tape player set in the SP mode, and in the event that the reading of both of the remaining tape hour display unit 15 and the recording time display unit 16 shows that the remaining tape hour Ts is smaller than the balance of the preset recording time less the length of time actually spent in the information recording, the operator has to manipulate the tape transport speed selecting switch 20 to set the magnetic tape player in the EP mode, that is, to cause the magnetic recording tape 1 to be transported at the extended speed. On the other hand, in the event that, during the EP mode in which the magnetic recording tape 1 is transported at the extended speed, the value equal to a multiple of the remaining tape hour Ts coincides with the balance of the preset recording time less the length of the time actually spend in the information recording as indicated by the display unit 16, the manipulation of the tape transport speed selecting switch 20 may result in that the information recording to the end of the magnetic recording tape 1 can terminate simultaneously with the zeroing of the preset recording time, thereby preventing a number of turns of the magnetic recording tape from being left on the supply reel which may be short of a length required to record the future program and, hence, may be unusable turns of the magnetic recording tape on the supply reel.
With the conventional magnetic tape player, when an attempt is made to maximize the utilization of the unrecorded portion of the magnetic recording tape in such a way as to avoid the unusable turns of the magnetic recording tape on the supply reel about the end of the magnetic recording tape or to avoid the possibility that the end of the magnetic recording tape is approached during the course of information recording taking place thereby leaving a portion of the information unrecorded, the operator of the magnetic tape player has to read the respective displays on the separate display units and perform and mentally compare the remaining tape hour with the balance between the preset recording time and the length of time actually spent in information recording to determine the necessity of the manipulation of the tape transport speed selecting switch. Accordingly, inconvenience has been often experienced with the conventional magnetic tape player that the operator cannot leave the area where the magnetic tape player is installed.